In the Third Generation Partnership Projects (3GPP), a mobile communication system based on Code Division Multiple Access (CDMA) technology has been specified, which is referred to as a “Wideband-Code Division Multiple Access (W-CDMA) System.” The mobile communication system (which is referred to as “3G,” hereinafter) is widely adopted in many countries, which include Japan and European countries, for example. The W-CDMA system is also referred to as a “Universal Mobile Telecommunications System (UMTS).” For a system based on a Long Term Evolution (LTE) scheme, specifications have been defined so that a higher data rate, a greater capacity, and lower latency are achieved compared to those of the communication system based on the 3G scheme. For the LTE system, Orthogonal Frequency Division Multiplexing (OFDM) technology has been specified. Each of the various types of the radio communication systems is referred to as “Radio Access Technology (RAT).” In addition to the radio communication systems based on the W-CDMA scheme and the LTE scheme, the RATs include radio communication systems based on the CDMA2000 standard and the GERAN standard, for example. These RATs are operated, by various operators, in various countries and regions, with various frequencies. For some cases, a plurality of RATs may be operated in a same area. In such a case, for attempting to distribute load on some RATs, or for a case in which a user requests a service which is only provided in a specific RAT, for example, a process is executed which causes a user to transfer from one specific RAT to another RAT.
For example, supposed that a voice communication service is not provided in a particular RAT, which is based on the LTE scheme, and that a user connected to the RAT requests the voice communication service. In this case, it may be necessary to transfer the user to a RAT, which is based on the 3G scheme, and provide the voice communication service to the user. Such a technique is referred to as “CS Fallback (CSFB).”
One method of switching a connection destination among a plurality of different RATs is a method which is called redirection (Release with Redirection). When it becomes necessary to transfer a user (mobile station) in a RAT to another RAT, a network (NW) transmits a release redirection control signal to a mobile station. The release redirection control signal includes information indicating a destination RAT and a frequency which is used in the destination RAT. The release redirection control signal is a RRC message (RRC Connection Release), which is for reporting that the connection with a current RAT is to be terminated and a connection with a switching destination RAT is to be established. The mobile station that receives the release redirection control signal (RRC Connection Release) terminates the connection with the current RAT; searches for a cell, whose frequency is specified as the switching destination; obtains a synchronization signal; retrieves broadcast information from the switching destination cell; and establishes connection with the switching destination cell. In this manner, the mobile station is served in the switching destination cell. For example, the mobile station can receive a service, which is provided in the switching destination RAT.
A technique is known such that a part of broadcast information (Master information Block: MIB) and a System Information Block (SIB), which are transmitted in the switching destination RAT, is included in the release redirection control signal (RRC Connection Release) so as to reduce a switching time period during the redirection of the mobile station between the RATs. Some specifications of the 3GPP specify this technique, and it is called “Release with redirection with SIB” (cf. Non-Patent Document 1 and Non-Patent Document 2 for this point). Since the mobile station which receives the release redirection control signal can reduce the time period required for retrieving the broadcast information, the switching of the RAT can be executed, while reducing at least the corresponding amount of time. The quick switching of the RATs is desirable in a point that, for example in the CSFB, the voice communication service can be quickly provided by quickly switching the RAT from the LTE scheme to the 3G scheme, after receiving a request for the voice communication from the user. When the RAT is switched by this method, a connection request signal (RRC Connection Request) to be transmitted by the mobile station to a base station of the switching destination RAT includes a predetermined indicator (System Information Container Stored Indicator), which indicates that the mobile station is operating in accordance with the “Release with Redirection with SIB.”